3D-Printing of Pure Metal–Organic Framework\nMonoliths

Abstract

Metal–organic\nframeworks (MOFs) are usually synthesized\nin powder form. For many practical applications, MOFs need to be shaped\ninto monoliths that can be easily handled. However, conventional shaping\nmethods, such as pelletization, often result in a decrease in functionality.\nRecently, MOF-containing monoliths have been made using direct ink\nwriting (DIW; extrusion 3D printing), but to date, high additive loadings\nhave been required. In this work, we demonstrate that colloidal gels\ncontaining only ethanol and Cu₃(BTC)₂ (BTC =\n1,3,5-benzenetricarboxylate) (HKUST-1) nanoparticles can be used directly\nas an ink for the DIW of pure densely packed and self-standing MOF\nmonoliths. The MOF gel shows ideal rheological properties for 3D extrusion-based\nprinting, suggesting this method may be generalized to other MOF families\nthat form gels. Importantly, the accessible porosity and surface area\nof the MOF is retained well after shaping. The 3D printed HKUST-1\nmonolith displays an exceptionally high BET surface area of 1134 m²/g, and a high mesopore volume. We demonstrate that for methane\nstorage, a classical application of HKUST-1, the 3D printed monolith\nis comparable or superior to monoliths formed by other shaping methods.